This application is based on Patent Application Nos. 2000-351999 and 2000-352004 both filed Nov. 17, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus. More specifically, the present invention relates to a system for minimizing an effect the mist of ink, processing liquid for rendering the ink insoluble or insolubilized substance has on an ejection performance of print heads during a printing process that uses the ink and the processing liquid, the mist being produced as a result of injecting the ink and the processing liquid.
2. Description of the Related Art
The processing liquid that renders ink insoluble basically contributes to improving the water resistance of a printed image. The processing liquid is ejected onto the same areas of a print medium where the ink droplets have landed so that droplets of the processing liquid overlap the ink dots, or onto those areas adjacent to the ink dots so that they partly contact the ink dots. The resulting mixing of the ink and the processing liquid causes a colorant in the ink to become insoluble. The ink fixed on the print medium in this way has improved water resistance because of its insolubility.
In addition to this purpose, the processing liquid is also used to improve the quality of a printed image. In this regard, the applicant of this invention has made a variety of proposals. For example, the processing liquid is effective for preventing feathering and spreading of ink and for improving the density.
The processing liquid is ejected by using ordinary print heads similar to those used for ink. In the case of a serial type printer, for example, a processing liquid head is mounted on a carriage along with black, cyan magenta and yellow heads. As the carriage moves, the ink or the processing liquid is ejected onto the print medium from respective heads in the order of their arrangement. In a printer with so-called full-line type heads each having ejection nozzles arrayed over a range corresponding to a width of the print medium, the processing liquid head and the ink ejecting heads are arranged at predetermined intervals in the print medium feed direction. The processing liquid is ejected after each feeding of the print medium, resulting in the processing liquid being mixed with the ink on the print medium as described above.
In the ink jet printing apparatus using the processing liquid, however, because the processing liquid renders the ink insoluble, insolubilized substances not directly involved in the printing are produced and may have a variety of adverse effects on the printing.
To describe in more detail, when the processing liquid is ejected from the head, not only are droplets formed that are intended to land on the print medium but much smaller droplets or mist are also produced. The mist of the processing liquid, because it has relatively small mass and speed, may not reach the print medium but float and adhere directly to the nozzle surfaces of other heads. The nozzle surface is a surface of the print head in which the ink ejection nozzles are arranged. When the floating mist of the processing liquid adheres to the nozzle surfaces and reacts with the ink in or around the nozzles to form insoluble substances, ejection troubles may arise such as ink ejection failures, insufficient amounts of ink ejected and deviations of ink ejection directions.
The processing liquid mist may also be produced by a part of the ejected processing liquid droplets bouncing off the print medium when they land on it. Such bounced-off mist of the processing liquid may adhere to other heads, leading to similar ejection failures.
The ejection failure due to the insolubilized substances may be forestalled by performing ejection performance recovery operations, such as wiping, preliminary ejection and nozzle suction by vacuum, to remove the unwanted mist adhering to the nozzle surface. However, since these recovery operations are not able to be performed during the printing operation, they basically lower the throughput of the print output. Hence, on top of the ordinary ejection performance recovery operations, executing additional operations for eliminating the ejection troubles due to the mist described above may bring about an unacceptable, significant reduction in the throughput.
The present invention has been accomplished to solve the above-described problems and provides an ink jet printing apparatus which can reduce the adverse effect the mist of the processing liquid or the insoluble substances formed by the processing liquid has on the ejection performance of the ink or processing liquid head during the process of printing that uses the ink and the processing liquid for rendering the ink insoluble.
According to one aspect, the present invention provides an ink jet printing apparatus which comprises: at least one ink head for ejecting an ink; a processing liquid head for ejecting a processing liquid, the processing liquid being adapted to render a colorant of the ink ejected from the ink head insoluble; and a diffusion means provided near the processing liquid head to diffuse mist of the ink and/or processing liquid ejected from the ink head and/or processing liquid head; wherein the ink head and the processing liquid head are moved relative to a print medium and eject the ink and processing liquid onto the print medium to perform printing.
In this invention, the diffusion means includes a head holding means, which holds and arranges a plurality of ink heads and a processing liquid head in a direction in which they move relative to the print medium and, in this arrangement, places the processing liquid head between the ink heads in such a way that a distance between the processing liquid head and the print medium is larger than any of distances between the plurality of ink heads and the print medium.
In this construction, because the processing liquid head is arranged between the ink heads and has a larger distance to the print medium than those of the ink heads, the processing liquid mist that may be produced as a result of ejection of the processing liquid mainly diffuses into the recessed space formed by the arrangement of these heads. Thus, the processing liquid mist hardly reaches the nozzle areas of the ink heads. Further, since the processing liquid head has a large distance to the print medium, the chances that the mist bounced off the print medium which includes insolubilized substances may reach the nozzle area of the processing liquid head can be reduced.
Hence, in the ink jet printing apparatus which performs printing by using the ink and the processing liquid that renders the ink insoluble, it is possible to reduce the effect the mist of the processing liquid or substances insolubilized by it has on the ejection performance of the processing liquid head.
In other words, this invention has been accomplished in light of the fact that the landing accuracy of the processing liquid does not have to be as high as those of the inks. That is, unlike the inks, the processing liquid does not directly form pixels and is not required to land with high precision on the intended positions on the print medium. The processing liquid therefore need only have a landing accuracy that will cause the landed processing liquid to mix with the ink dots to produce a predetermined level of an insolubilizing reaction.
The present invention therefore sets the head-to-paper distancexe2x80x94one of factors that determine the landing accuracyxe2x80x94of the processing liquid head larger than those of other heads, as described above, to form a recessed space between the ink heads adjoining the processing liquid head on both sides so that the processing liquid mist from the processing liquid head can diffuse or escape into this space, thus preventing the mist from reaching the nozzle surfaces of the other heads. The recessed space can also reduce the amount of the bounced-off mist generated by the ejection of the processing liquid that may adhere to the processing liquid head.
Further, the present invention is characterized in that the diffusion means has a head holding means, which holds and arranges a plurality of ink heads and the processing liquid head in such a way that a distance between the processing liquid head and an adjoining ink head is larger than a distance between other adjoining ink heads.
According to another aspect, the present invention is characterized in that the diffusion means has a head holding means, which holds the at least one ink head and the processing liquid head in such a way that a distance between the processing liquid head and an adjoining ink head is large enough to allow mist resulting from an ejection of the processing liquid from the processing liquid head to diffuse into a space defined by the distance.
According to still another aspect, the present invention is characterized in that the diffusion means comprises: a head holding means for holding the at least one ink head and the processing liquid head; and an air flow control means for controlling an air flow to diffuse mist, resulting from an ejection of the processing liquid from the processing liquid head, into a space formed between the processing liquid head and the ink head held by the head holding means.
According to one aspect of this invention, because the distance between the processing liquid head and the adjoining ink head is set larger than those between other ink heads, the mist produced from the ejection of the processing liquid and the mist produced by the ejected processing liquid bouncing off the print medium can be diffused in the space defined by the relatively large head-to-head distance. It is therefore possible to prevent the mist from adhering to the nozzles of the adjoining ink heads and the resultant insolubilized substances from causing an ejection failure of the ink heads.
According to another aspect of this invention, because the distance large enough to allow the diffusion of the mist is provided between the processing liquid head and the ink head, it is similarly possible to prevent the mist from adhering to the nozzles of the ink heads and the resultant insolubilized substances from causing an ejection failure of the ink heads.
According to a further aspect of this invention, because an air flow is generated in the space between the processing liquid head and the ink head to diffuse the mist, it is similarly possible to prevent the mist from adhering to the nozzles of the ink heads and the resultant insolubilized substances from causing an ejection failure of the ink heads.
As a result, the effect the processing liquid mist has on the ejection performance of the ink heads can be reduced, thus assuring good printing without any ejection failure.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.